Updated: Apr 16, 2019
Want a healthy, and great-looking lawn year round? Try over-seeding!
Over-seeding is an important part of growing a healthy, lush lawn. Over-seeding can revive plants damaged by lack of water, heavy foot traffic or heat. Over-seeding not only allows grass to grow where it doesn’t exist, but it also improves the lawn by sowing better varieties. The process of over-seeding involves planting grass seed directly into the existing turf, without ruining the turf or soil. Still need another reason? If you don’t over-seed, you run the risk of weeds overtaking your lawn.
Fall is the ideal time to over seed cool season grasses, because the soil is still warm enough to germinate seeds and the cool air invites grass to grow a strong root system. Cool season grasses include Kentucky Bluegrass, Perennial Rye grass and Fescue. For spring, warm season grasses include Bermuda, Centipede, Saint Augustine and Zoysia.
Your geographic location affects when and how you over seed. Cooler fall weather happens earlier in the North; therefore, you should over-seed your cool season grasses by late summer or early fall if you live in this region. Late spring or early summer is ideal for over seeding warm season grasses in the South.
If you’re like us, and live in a warmer region but like green grass all year long, you can try over seeding your Bermuda grass, which turns brown in the fall, with fescue, or another variety of “Cool Grass” that will continue your lawn's color well into the cooler months.
There are a few things to keep in mind before you over seed:
• Know the measurements of your lawn. Multiply the width and length of your lawn space to calculate the square footage. If you have multiple areas to cover, divide each section, do the calculation, and then add the sums together for the total square footage.
• Stop fertilizing for at least a month before over-seeding. Vigorous growth of the existing lawn will make it more difficult for new seeds to establish themselves.
• Identify your grass type, so you can treat it appropriately. To do this, examine the climate of your growing region, look at the shape of the grass blades, feel the texture of the grass, and/or take samples to your local Home Depot Garden Center for assistance.
• Consider doing a soil test if you don’t know the pH level of your soil. This will help you determine the conditions of your soil so you can apply the appropriate nutrients to it. Test your soil using a soil test kit or take samples to your local extension service or state university to analyze.
• Most important: do NOT use a pre-emergent prior to over-seeding; While the pre-emergent kills and keeps weed seeds from growing, it will also prevent grass seeds from germinating. I always recommend that people wait at least 6 weeks before applying pre-emergent, until after over seeding is complete.
Mow & Dethatch to Prepare Your Lawn
Mow your lawn so that the grass sits above the soil line. Ideally, it should stand at an inch to an inch and a half. This will allow your grass seed to get adequate sunlight and connect with the soil.
Next, use a thatch rake or power rake to remove any thatch that you find, a process called detaching. Thatch is a spongy layer of dead organic matter mixed with living plant parts that can lead to disease and insect problems if not eradicated. A heavy layer of thatch can prevent your grass seeds from germinating.
To dethatch, rake the lawn in one direction and give it another pass in the opposite direction. The tines on the rake will pull up the thatch along the way. Be sure to rake the thatch off the lawn when you’re done.
Aerate your lawn
Another way to remove thatch is to aerate your lawn. This combs your grass and kicks out debris. It also loosens the soil so that air and water can reach the roots. Your grass seed will be able to grow faster and more robust. Lawns that are compacted due to heavy foot traffic should especially be aerated to produce efficient growth.
A core aerator is a great tool for this job. You can rent one at your local Home Depot store.
To operate the core aerator, move it across the lawn in straight lines until the yard is fully covered. Do a second pass perpendicular to the first one if needed. Make sure the core aerator pulls plugs of soil from the turf rather than simply punching holes in the ground. This helps to break up the compaction. Leave the plugs to dissolve on their own within a couple weeks.
Improve weak spots
If your lawn has bare areas, spot treat it with topsoil, which will improve the quality of the soil and allow new grass to grow.
Have water drainage problems preventing grass growth? Apply a thin layer of sand over it and smooth it out with a rake. Sand allows the grass to germinate faster and it creates a thicker root zone.
Over seed and fertilize your lawn
• After you have prepped your lawn, spread your grass seeds evenly using a broadcast spreader, drop spreader or hand spreader. Follow manufacturer’s instructions for distributing the seeds.
• Then, apply slow-release fertilizer that works best for your specific grass. Slow-release fertilizer provides nutrients to plants gradually, within three months in many cases. This will prevent you from over-fertilizing.
• Lightly water the lawn immediately after over seeding. Continue to water it frequently, about three to four times daily for the first several weeks to ensure proper germination.
• Once the grass is an inch tall, cut the frequency of watering back to once a day, but increase the duration of watering to 20 to 30 minutes per zone.
Maintain Your Rejuvenated Lawn
• Continue to mow the grass to a height of two inches for the remainder of the season. Mow the lawn when the grass is dry.
• Fertilize the lawn about six weeks after you sow the seed. Apply a pound of quick-release nitrogen fertilizer for every thousand square feet of lawn space. Repeat this process in another six weeks.